By Lars Mucklejohn BP and Shell are expected to post lower profits this week as the supermajors grapple with weak oil prices and a global slowdown in demand. BP is due to publish its third-quarter earnings on Tuesday, while Shell will report its results on Thursday. Earlier this month, the FTSE 100 firms warned of falling profit margins at their oil refining businesses – major parts of their income streams. The slump in margins came amid a broader faltering in demand for oil across consumer and industrial sectors, with brent crude prices staying broadly flat since the start of 2024. Prices hav…